As a disk recording medium device in which a disk-like recording medium capable of recording and/or reproducing information such as audio data, video data or computer data is accommodated within a cartridge housing so as to become freely rotatable, there is known a disk recording medium device having an arrangement shown in FIG. 51, for example. This disk recording medium device 1 is an information recording media which incorporates therein a write once magneto-optical disk on which users are able to record (write) information such as computer data later on.
This disk recording medium device 1 comprises a cartridge housing 2 composed of a pair of upper shell 2a and lower shell 2b, a magneto-optical disk 4 accommodated within a disk compartment 3 of this cartridge housing 2 so as to become freely rotatable and so forth. The cartridge housing 2 has on its upper and lower surfaces provided an upper and lower opening portion 5 that extends from a central portion to one side. This opening portion 5 can be opened and closed by a shutter member 6 that can slide along one side. This shutter member 6 includes a pair of shutter members 6a opposing to each other in the plane direction. The shutter member is constantly spring-biased in the direction to close the opening portion 5 under spring force of a spring, not shown. Reference numeral 8 denotes a presser member for preventing a tip end portion of each shutter member 6a from being disengaged from the opening portion inadvertently.
The magneto-optical disk 4 has at its central portion provided a disk-like center hub 7 made of metal. This center hub 7 is located at the position opposing to the inner end portion of the opening portion 5, i.e. located at substantially the central portion of the cartridge housing 2. A turntable provided on the main body side of an information recording and reproducing apparatus is mounted to the center hub 7. The magneto-optical disk 4 is chucked to the turntable and thereby the magneto-optical disk is rotated at predetermined velocity (e.g. constant linear velocity). At that time, a magneto-optical pickup device of which the head portion is inserted into the opening portion 5 functions to record or reproduce information on or from the magneto-optical disk 4.
However, in the conventional disk recording medium device having the above-mentioned arrangement, the shutter member 6 is movably attached to the cartridge housing 2 that is composed by combining the upper shell 2a and the lower shell 2b. The opening portion 5 is closed by properly positioning the shutter members 6a of this shutter member 6 to the opening portion 5 and a dust-proof property is maintained by overlapping the peripheral edge portions of the shutter members 6a upon the peripheral edge portion of the opening portion 5. Thus, dusts, smudges and the like can be prevented from entering into the disk compartment 3. As a result, due to defects such as clearances produced when the shutter member 6 is assembled and warping of the shutter members 6a, it is unavoidable that clearances are produced between the peripheral edge of the opening portion 5 and the shutter member. There arises a problem that a dust-proof property will be deteriorated.
In recent years, as a storage capacity of optical disks is progressively increasing and a recording density is increasing more, a pitch in recording patterns is becoming narrower and a linear density is increasing more. For this reason, when an information recording surface of a magnetic recording medium such as an optical disk and a magneto-optical disk is smudged by dusts and the like, a trouble occurs in read and write of information by an optical pickup device and the optical pickup device becomes unable to read and write information normally.
However, as a storage capacity of optical disks is further increasing and a recording density is further increasing, even very small dusts and smudges that had not exerted a serious influence so far become more influential to read and write of information. Therefore, the disk cartridge that has been formed only by combining the upper and lower shells 2a, 2b was unable to prevent entrance of dusts and smudges of extremely small sizes. In this case, when the information recording surface of the magneto-optical disk 4 is smudged by very small dusts and smudges entered into the cartridge housing 2, the information recording surface is placed in the similar state in which it is damaged by dusts and smudges so that information cannot be read out from and written in the information recording surface normally.
In view of the aforesaid aspects, it is an object of the present invention to provide a disk cartridge, a disk recording medium device and a disk recording and/or reproducing apparatus in which concave and convex portions are provided on respective joint portions of a pair of shutter members joined to each other over the total length and a pair of shutter members is closed by engaging their concave and convex portions with each other so that a dust-proof property of a pair of shutter members for opening and closing the opening portion provided on the cartridge housing can be improved.